The present invention refers to a method of producing a nonwoven material comprising at least one layer of continuous filaments, such as spunbond- or meltblown filaments.
Nonwoven materials are produced in many different ways, at which fibres either in the form of continuous filaments or staple length fibres are laid as a web on a wire or other permeable carrier element, and are bonded together with an appropriate bonding technique. The fibrous web can be dry laid, wet laid or foam formed, the latter involving that the fibres are kept dispersed in a foam. Bonding may be provided by the fact that the fibres or filaments as they are laid on the wire are still hot and will adhere to each other. It is also possible to heat the fibrous web from the outside so that at least a part of the fibres or filaments in the fibrous web are melted to become adhering. Bonding can also be provided with different types of chemical bonding agent or mechanically. The latter includes techniques like needling and so called hydroentangling or spunlacing, which involves that the fibres are entangled by means of very fine water jets under high pressure. Several rows of water jets are directed against the fibrous web, which is supported by a moveable wire. The entangled fibrous web is then dried. The fibrous web may either by dry laid, wet laid or foam formed. Spunlace materials may be produced in high qualities at a reasonable cost and have a high absorptive capacity. They are used for example as wiping material for household or industrial use, as disposable material in healthcare and hygiene etc.
Through for example EP-B-0 333 211 and EP-B-0 333 228 it is known to hydroentangle a fibrous mixture in which one of the fibrous components are meltblown fibres or filaments. The base material, i.e. the fibrous material that is exerted to the hydroentanglement, either consists of two pre-shaped fibrous layers wherein one layer consists of meltblown fibres or of a so called coform material in which an essentially homogeneous mixture of meltblown fibres and other fibres are air laid on a wire and then exerted to hydroentanglement.
Through WO 99/22059 it is known to foam form a fibrous web of natural fibres and/or synthetic staple fibres and to hydroentangle the foamed fibrous dispersion with continuous filaments, such as meltblown- or spunbond fibres, for forming a composite material in which the continuous filaments are well integrated with the other fibres.
When laying continuous filaments, such as spunbond- or meltblown fibres, on the permeable support member, e g the wire, it is necessary to quickly remove the air between the filaments. The wire should thus have high air permeability and an open structure. If short fibres, e g synthetic staple fibres or pulp fibres, are then to be laid on top of the continuous filaments, it is however desired to have a tighter wire structure in order to avoid loss of a considerable amount of the short fibres during drainage. However the drainage capacity should be sufficient to provide an effective drainage of the fibrous web. One way of solving the problem of having a very open wire with high air permeability when laying the continuous filaments and a tighter wire when laying the shorter fibres is of course to form the different fibrous webs on different wires. This is however costly and makes the process expensive and complicated
The object of the present invention is to provide a method of producing a nonwoven material comprising at least one layer of continuous filaments, such as spunbond- or meltblown fibres, and wherein the problem of laying the continuous filaments on a wire having a very open structure and a high air permeability, while the continued process, such as bonding of the fibrous web and/or combining it with other fibres, is made on a wire having a tighter structure. This has according to the invention been provided by laying a first web of continuous filaments on a wire or other permeable support member having a resilient extensibility in the transverse direction and which substantially resumes its original dimension when the extension is discontinued, that the wire is stretched in the transverse direction to at least 120% of its original width when the continuous filaments are laid on the wire, that the stretching is discontinued after the continuous filaments have been laid on the wire.
Preferably the wire is stretched in the transverse direction to at least 130%, more preferably to at least 150% of its original width when the continuous filaments are laid on the wire.
According to a preferred embodiment of the invention a second web of natural and/or synthetic staple fibres is laid on top of said first web of continuous filaments after the stretching has been discontinued. This second fibrous web may contain cellulose fibres.
Said second fibrous web may be dry-, wet- or foam formed
According to a preferred embodiment the different fibrous webs are hydroentangled together to form a composite material, in which the different fibre types are well integrated with each other.